The present invention relates to joints for sheet material and to methods of joining sheet material, and in particular to joints for sheet metal and to methods of joining sheet metal.
It is known to join sheet metal components by welding an edge of one sheet metal component to the face of an adjacent sheet metal component, or by firstly bending the end of one sheet metal component and welding the face of the bent over end of the first metal component to the face of an adjacent sheet metal component. It is known that other types of bonding may be used for example brazing, soldering or adhesive.
It is also known to join sheet metal components by firstly bending over the end of one sheet metal component and riveting the face of the bent over end of the first sheet metal component to the face of an adjacent sheet metal component. The rivets are separate fixing devices of circular cross-section inserted through circular cross-section apertures in the metal sheets. It is also known that other types of mechanical attachment may be used for example nuts and bolts.
It is further known to join sheet metal components by firstly providing one or more projections from the edge of one of the sheet metal components, providing a corresponding number of slots through the adjacent sheet metal component and passing the projections on the first metal sheet through the slots in the adjacent sheet metal component. It is known that the projections are then either bent over to abut the opposite face of the adjacent sheet metal component or the projections are twisted to prevent the projection withdrawing from the slot.
A problem with the welded, brazed or soldered joint is that these are hot joining processes which may require subsequent costly heat treatment of the sheet metal components.
A problem with the fold over projection joint or the twist projection joint is that they are not used in joints which are required to transmit or resist external loads. The fold over projection joint, or the twist projection joint, is normally used to simply maintain the relative positions of an assembly of sheet metal components. The fold over projection and twist projection have a tendency to unfold, untwist or deform such that the joint becomes loose.
The present invention seeks to provide a novel rivet type joint for sheet material.
Accordingly the present invention provides a joint for joining a first ductile sheet to a second ductile sheet comprising at least one deformable projection on an edge of the first ductile sheet, the at least one deformable projection having an aperture therethrough to define two sides, a base and a head of the deformable projection, the base interconnecting the sides of the deformable projection, the head interconnecting the sides of the deformable projection, at least one aperture extending through the second ductile sheet, the at least one deformable projection on the first sheet extending through the at least one aperture in the second sheet, the head of the deformable projection being deformed such that the head expands at least a portion of each side of the deformable projection beyond the sides of the at least one aperture to prevent withdrawal of the deformable projection from the aperture in the second ductile sheet, the base of the deformable projection extends a predetermined distance into the at least one aperture in the second ductile sheet, the deformable projection and the aperture through the deformable projection are shaped and configured such that deformation of the head fills the aperture.
Preferably each side of the deformable projection has a dog extending away from the other dog such that deformation of the head expands the dog of each side of the deformable projection beyond the sides of the aperture to prevent withdrawal of the deformable projection from the aperture in the second ductile sheet.
Preferably the head expands the remainder of each side of the deformable projection into contact with the sides of the aperture.
Preferably the undeformed head tapers away from the edge of the first sheet.
Preferably the aperture is a slot. Preferably the deformable head and the slot are rectangular in cross-section.
Preferably the deformable head and the portion of each side of the deformable projection are arranged such that they are located at, or greater than, a predetermined distance from the edge of the first ductile sheet, the predetermined distance is the thickness of the second ductile sheet.
Preferably the first ductile sheet has a plurality of deformable projections and the second ductile sheet has a plurality of apertures.
The present invention also provides a method of joining a first ductile sheet to a second ductile sheet comprising forming at least one deformable projection on an edge of the first ductile sheet, forming an aperture through the at least one deformable projection to define two sides, a base and a head of the deformable projection, the base interconnecting the sides of the deformable projection, the head interconnecting the sides of the deformable projection, forming at least one aperture extending through the second ductile sheet, inserting the at least one deformable projection on the first sheet extending through the at least one aperture in the second sheet, deforming the head of the at least one deformable projection such that the head expands at least a portion of each side of the deformable projection beyond the sides of the at least one aperture to prevent withdrawal of the deformable projection from the aperture in the second ductile sheet, forming the base of the deformable projection such that it extends a predetermined distance into the at least one aperture in the second ductile sheet, forming the deformable projection and the aperture through the deformable projection such that they are shaped and configured so that deformation of the head fills the aperture.
Preferably the method comprises forming a dog on each side of the deformable projection, each dog extending away from the other dog such that deformation of the head expands the dog of each side of the deformable projection beyond the sides of the aperture to prevent withdrawal of the deformable projection from the aperture in the second ductile sheet.
Preferably the method comprises forming the undeformed head such that it tapers away from the edge of the first sheet.
Preferably the method comprises forming a slot in the second ductile sheet.
Preferably the method comprises forming the deformable head and the slot such that they are rectangular in cross-section.
Preferably the method comprises forming the deformable head and the portion of each side of the deformable projection such that they are located at, or greater than, a predetermined distance from the edge of the first ductile sheet, the predetermined distance is the thickness of the second ductile sheet.
Preferably the method comprises forming a plurality of deformable projections on the first ductile sheet and a plurality of apertures in the second ductile sheet.
Preferably the method comprises forming the at least one deformable projection on the first ductile sheet by laser cutting.
Preferably the method comprises forming the at least one aperture in the second sheet by laser cutting.